1. Field of the Art
The various embodiments described herein relate generally to enhanced cellulosic fibers having a modified morphology suitable for use in a liquid distribution mat in an absorbent article. The mat made thereof has enhanced vertical wicking properties. When used in an absorbent article such as a baby diaper, the mat rapidly acquires and transports bodily discharges from the point of insult to other regions of the absorbent article, thereby maximizing the utilization of an absorbent structure.
2. Description of Related Art
Cellulose fibers are well known and are used in a wide variety of disposable absorbent articles such as diapers, incontinence products, and feminine hygiene products. Disposable absorbent articles typically are made with an absorbent core made of a composite of cellulosic fluff pulp and superabsorbent polymer sandwiched between a liquid pervious top sheet, and a liquid impervious backsheet. An optional fluid distribution layer may be disposed between the top sheet and the absorbent core or between the back sheet and the absorbent core. The distribution layer may include a wide variety of materials, including, for example, cellulosic fiber, synthetic fiber, or a mixture of both.
Distribution layers typically are made by a wet-laid process, because wet-laid materials typically possess excellent tensile strength in the wet and dry states and high vertical liquid wicking. “Vertical wicking” as used herein refers to the ability of a material to draw fluids in a vertical direction against gravity. Vertical wicking is a desirable property since it indicates a material's ability to move fluid away from the point of contact, allowing more complete utilization of the absorbent article. As a result, a wearer of the absorbent article is left with a drier feel to the skin.
Several approaches for making a liquid distribution layer have been reported in the literature. Examples of liquid distribution layers include cellulosic foams, such as those commercially available from Spontex SA. France, or High Internal Phase polymerized materials such as those described in U.S. Pat. No. 5,268,224 (DesMarais), the disclosure of which is incorporated herein by reference, in its entirety. In an alternative approach, high surface area synthetic fibers have been applied in absorbent structures in order to improve the liquid distribution, such as described in U.S. Statutory Invention Registration No. H1511, the disclosure of which is incorporated herein by reference, in its entirety.
Other exemplary liquid distribution layers include cellulosic-fiber based materials, such as those disclosed in U.S. Pat. No. 3,575,174 and U.S. Pat. No. 4,781,710, the disclosures of which are incorporated herein by reference, in their entirety. In these materials, portions of the structure are compressed to a higher density, such as along “wicking lines” or in closed mesh patterns. These compressed portions have smaller pores that have increased wicking height. The creators of these materials also aimed at achieving a certain preferential fluid distribution direction. However, in these approaches the size of the large pores was reduced so much that the positive impact of the increased wicking height was counterbalanced by reduced amount of fluid which could be transported to such heights. Another approach to altering the pore size of distribution materials is described in U.S. Pat. No. 5,244,482 (the disclosure of which is incorporated herein by reference, in its entirety), in which reducing the maximum pore size of a fibrous structure containing meltable fibers is accomplished by stretching the fibrous structure in one direction and “freezing” the deformation by heat curing the fibers.
Other material composites have been developed that allowed for a more tailored pore size and pore size distribution. Exemplary materials are described in U.S. Pat. Nos. 5,549,589 and 5,800,416 (the disclosures of which are incorporated herein by reference, in their entirety), which provide a resilient structure made of specially stiffened cellulosic fibers, such as cross-linked cellulose fibers, in which the large pores of the structure are filled in with small and thin cellulosic fibers such as eucalyptus fibers. In both patents, thermoplastic fibers and chemical binders are added to the materials to provide sufficient integrity and strength to the material.
However, the aforementioned approaches are complex to manufacture and, hence, are relatively expensive. In addition, these technologies are still limited by the inverse relationship of wicking height and wicking flux, i.e. wicking height can be increased, but at cost of reduced wicking flux. As used herein, “wicking flux” relates to the amount of fluid being transported vertically through a certain cross-section of a distribution structure to a given height in a predetermined amount of time.
The description herein of certain advantages and disadvantages of known liquid distribution fibers and webs for use in absorbent articles, and methods of their preparation, is not intended to limit the scope of the embodiments described herein. Indeed, the embodiments may include some or all of the methods and materials described above without suffering from the same disadvantages.